1. Field of the Invention
This invention relates, in general, to the use of spare memory bits in large memory devices and more particularly to in-package electrically programmable redundant memory elements using E.sup.2 PROM devices.
2. Background Art
Bit density of integrated circuit memory devices has been increasing substantially over the past few years. As the bit density increases, the chance for device failure mode increases. Chip layout, inherent technological factors such as oxide failure, and random run-to-run process defect distributions such as broken polysilicon word lines may cause a failure mode of a memory array and its associated row and column decoders.
To overcome faulty memory elements in a device in order to provide yield enhancement, redundant to spare memory elements are included on the chip. Typically, the address of a faulty element is programmed into the spare element by either laser blowing or electrically blowing a polysilicon fuze within the element.
However, the laser blown method requires a special probe machine, special alignment of the laser, passivation opening over the fuze to be cut, re-passivation of the device after the fuze is blown, and a complex testing procedure. The typical electrical blown method requires excessively high power, a passivation opening over the fuze, and re-passivation after the fuze is blown. Both the laser and electrically blown methods could only be used for yield enhancement since they could only be accomplished at the wafer level of the process. The typical methods are only a one time, irreversible process that can not be erased.
Therefore, what is needed is an E.sup.2 PROM having an in-package electrically programmable redundant memory element that can be programmed and erased in the completed package with lower power.